1. Field of the Invention
The present invention relates to a surface pressure distribution sensor for detecting small irregularities of an object to be sensed.
2. Description of the Related Art
A surface pressure distribution sensor for detecting small irregularities in a surface of an object brought into contact with the sensor surface, as a pressure distribution, is described in, for example, Japanese Examined Patent Application Publication No. 7-58234 (corresponding to U.S. Pat. No. 5,400,662), showing a sensor for detecting the configuration of a coarse surface as data values.
As shown in, for example, FIG. 11, such a surface pressure distribution sensor includes a matrix of semiconductor switching devices 101, and electrodes 102 each connected with one end of each of the semiconductor switching devices 101. A flexible film coated with a conductor is formed so as to face electrodes on the opposing side of a semiconductor substrate with a certain spacing therebetween. A voltage is applied to the conductive coating. When an object having small irregularities is pressed against the flexible film, the film is deflected along the irregularities of the object. The conductive coating of the deflected film is brought into contact with the electrodes on the semiconductor substrate, thus allowing the matrix of the corresponding semiconductor switching devices to be activated in turn for detection.
Such a surface pressure distribution sensor of the related art includes a semiconductor substrate, but semiconductor substrates are generally expensive. In particular, when the surface pressure distribution sensor is used as a fingerprint detection sensor, the expensive semiconductor substrate must have an area large enough to be contacted with the finger, thus increasing the production cost. In addition, for the purpose of detection of small irregularities, stable contact between the exposed portion of the semiconductor switching devices and the conductive coating, which is caused by even a small pressure, must be maintained for a long period of time. However, in the surface pressure distribution sensor of the related art, it is difficult to maintain the contact area between the exposed portion of the semiconductor switching devices and the conductive coating clean for a long period of time.